Art can sometimes make people uncomfortable, but not everything that makes us uncomfortable qualifies as art. White on Black is an extraordinary document of life in Russia's institutions (the author went straight from a children's home to an old people's home - the only other option would have been a 'loony bin'). It is also scrappily written and frustratingly structured - even if saying so seems the equivalent of chiding someone who is writing in his own blood for mistakes in spelling.

Gallego was born in 1968 with severe cerebral palsy. It's easier to learn this, though, from the blurb than the book, where it's only mentioned halfway through. CP is not what you think of when reading the opening passage of the book: 'I'm a hero. It's easy to be a hero. If you don't have hands or feet, you're either a hero or dead.' In a later passage, his hands and feet are described as merely 'crooked'. Just as Christy Brown could control his left foot, Ruben Gallego can use his left index finger to press the keys of a computer.

The colouring Gallego inherited from his Spanish ancestry made him unpopular with some of the attendants in children's homes. They referred to his mother as a 'black-assed bitch', seeing her as a selfish exotic who had left her disabled child to be cared for by honest Russian women. In fact it was his grandfather, the secretary-general of the Spanish Communist party, who had done the dumping, telling the boy's mother that he had died. Again, this information comes from the blurb, though an extended passage in one section, in which Gallego as a child fantasises about his famous grandfather visiting him in the home, bringing a painting by his good friend Picasso, makes no sense without it. It has to be said that the passage doesn't make very much sense even with the background information, since as a child Gallego knew nothing about his ancestry. This is one of the moments in the book when the urge to be literary, rather than simply to bear witness, misfires.

At other times the fault is not over- but under-writing (or at least under-dramatising). It's hard to imagine a scene of greater poignancy than an old woman climbing over the fence of a children's home and fastening on the boy Ruben, lying in the garden, virtually force-feeding him blinis, repeating as she does so 'Pray for Auntie Varvara', until she's chased off by the staff. The impact is considerably muffled when the event is introduced like this: 'In Russia, there's a custom of honouring the dead by sharing food. On the fortieth day after someone dies, his relatives are supposed to share food - and not just with anyone they happen across, but with the most unfortunate. The more unfortunate the person fed, the more you've pleased the deceased and the greater your merit before God. But where was one to find them, the unfortunates, in the most fortunate country in the world?' Hindsight takes the edge off the intense emotions of the incident, all the thrill and alarm of this nurturing witch.

The subjective audit of Russia's children's homes isn't entirely unfavourable. There was tenderness to be had as well as neglect, humanity as well as kowtowing to bureaucracy. The kids who couldn't walk were left out of many activities but might be the only ones with a television. The children could be harshly teasing with newcomers but they too had an enlightened side, sharing their tea and vodka (discouraged for those under 12). The education on offer would compare favourably with many countries, including this one. A nine-year-old doesn't acquire the ability to read Stanislaw Lem's Solaris in a day - if Gallego is to be believed - without a lot of help, as well as an older boy willing to lend him a copy.

Even so, Gallego wished he had been born in America, where (he had been told) the disabled were simply put down. (Later he visited the country and was deeply impressed with McDonald's.) There was euthanasia of a sort practised on disabled Russian children. If after 10 years of education they hadn't learned to make a living, hardly likely for those who couldn't walk, they would be transferred to an old people's home, where they would be unlikely to last more than weeks.

White on Black is written as a series of vignettes, not all of them first-person. In the third-person sketches Gallego displays that rare quality, the ability to sympathise with those more fortunate than himself. It's a loss, though, that crucial episodes of his own story are omitted, such as how he survived the old people's home when so many others died, and how he got out of it. It's disconcerting to read references early in the book to his two wives with no later account of how they came into the picture. In the case of someone so physically dependent, to break up with a partner is almost more impressive than finding one in the first place.

In a preface, the author defends the truthfulness of this account of his life, while also admitting to a bias towards positivity. 'I've witnessed too much human cruelty and hate. To describe the vileness of man's fall and bestiality is to multiply the already endless chain of interconnected blasts of evil. That's not what I want. I write about goodness, triumph, joy and love.'

It's true that there are queasy, Dostoevsky-meets-Pollyanna passages, where the uplift seems very forced. But few writers are more entitled to a sense of triumph. Again, this knowledge comes from the cover copy rather than the text. Ruben Gallego was reunited with his mother in 2000, and now lives with her in Germany. Many writers start from a sense of hurt, but very few succeed in writing themselves into fame, prosperity and the restoration of something they never had.